U.S. Secretary of State Rex Tillerson urged calm after North Korea and President Donald Trump traded threats, saying Americans should have "no concerns."

Tillerson, speaking to reporters shortly before arriving on the U.S. Pacific island of Guam on August 9, said he doesn't believe there is "any imminent threat" after North Korea had said that it is "carefully examining" plans to launch a missile strike on the island.

"Americans should sleep well at night," Tillerson said.

The North Korean threat to attack Guam came hours after U.S. Trump warned Pyongyang that it would face "fire and fury like the world has never seen" if it threatened the United States again.

Tillerson said Trump was trying to send a strong message to North Korea. He said Pyongyang's rhetoric had ratcheted up in the face of international opposition to its nuclear program.

"So I think...what the president is doing is sending a strong message to North Korea in language that Kim Jong Un would understand, because he doesn't seem to understand diplomatic language," Tillerson said.

Germany, meanwhile, has voiced deep concern and urged restraint following the sharp exchange of warnings.

​"We are watching the increasing rhetorical escalation regarding the Korean Peninsula with the greatest concern," German Foreign Ministry spokesman Martin Schaefer told reporters. "That is why we call on all sides to use restraint."

Schaefer said Germany is convinced that a "military option" could not be "the answer in the quest for a nuclear weapon-free Southeast Asia."

North Korea has said its goal is to develop a nuclear-tipped missile capable of striking the United States and has shrugged off international sanctions aimed at forcing it to halt its nuclear and missile programs.

In a statement carried by the state-run KCNA news agency, a spokesman for North Korea's army said that a strike by a medium- to long-range strategic ballistic missile could be launched toward Guam at any moment once leader Kim Jong Un makes a decision.

The spokesman said the strike would aim to "contain the U.S. major military bases on Guam." Guam is a critical outpost for the United States to launch military missions in the Asia-Pacific region.

North Korea also accused the United States of preparing a "preventive war" that it said would turn into an "all-out war wiping out all the strongholds of enemies, including the U.S. mainland."

The North Korean statement came after Trump, speaking at a news briefing on August 8 during his vacation in the U.S. state of New Jersey, said that "North Korea best not make any more threats to the United States."

"They will be met with fire and fury like the world has never seen," Trump said.

Japanese Chief Cabinet Secretary Yoshihide Suga said on August 9 that the "United States has said that all options are on the table. The Japanese government supports this attitude."

Guam Governor Eddie Calvo dismissed Pyongyang's threat and said the island was prepared for "any eventuality" with strategically placed defenses.

Calvo said he had been in touch with the White House and there was no change in the threat level for Guam, whose population is about 163,000.

In a video message, Calvo said "Guam is American soil...We are not just a military installation."

Trump issued his warning to North Korea after a Washington Post report said Pyongyang had produced a miniaturized nuclear warhead that can fit inside its missiles -- a key step in the country's attempt to become a full-fledged nuclear power.

The rhetoric between the White House and Pyongyang has heated up dramatically after North Korea tested two intercontinental ballistic missiles in July, taking a significant step toward its goal of developing a long-range missile capable of striking anywhere in the mainland United States.

The UN Security Council on August 5 unanimously imposed new economic sanctions on North Korea, aimed at pressuring Pyongyang to end its nuclear program.

North Korea said the sanctions infringed its sovereignty and warned that it was ready to give Washington a "severe lesson" with what it called its strategic nuclear force in response to any U.S. military action.

On August 8, The Washington Post reported that U.S. intelligence officials assess that North Korea has produced nuclear weapons for ballistic missile delivery, including by intercontinental missiles.

The article, citing unnamed U.S. intelligence officials, said the confidential analysis was completed by the U.S. Defense Intelligence Agency last month.

It said it was not known if North Korea had successfully tested the smaller warhead design, although North Korea last year claimed to have done so.

The Washington Post also reported that another intelligence assessment estimated that North Korea now has “up to 60 nuclear weapons,” more than previously thought.

In Tokyo, the Defense Ministry of Japan, a key U.S. ally, concluded in an annual white paper released on August 8 that "it is possible that North Korea has achieved the miniaturization of nuclear weapons and has developed nuclear warheads."

North Korea has ignored global calls to halt its nuclear and missile programs. It says its ballistic missiles are a legitimate means of defense against perceived U.S. hostility and accuses Washington and Seoul of escalating tensions by conducting military drills.

Meanwhile, U.S. Secretary of State Rex Tillerson held talks with Malaysian officials on August 9, as part of a Southeast Asia trip designed to persuade allies to maintain pressure on North Korea over its nuclear missile program.

In Germany, Schaefer backed Tillerson's call to resume talks with Pyongyang if it halts ballistic-missile tests.

"We must all continue our diplomatic efforts -- it is the only way to ensure that the threat of the illegal North Korean nuclear weapons program can be contained," Schaefer said.

He urged the international community to "thoroughly implement" the latest round of UN Security Council sanctions against North Korea.